1. Notes: Electric Circuits
Current, Voltage, Resistance,
Ohm’s Law, and Power
Physics 614

2. CURRENT ELECTRICITY
CURRENT ELECTRICITY is the controlled movement or flow of electric charges along a conductor.
An ELECTRIC CIRCUIT is a controlled path for the flow of electric current. There are 4 main components to most circuits: energy source, load, conducting wires, switch.

3. Electric Circuits

4. What Is Current? continuous flow of ________ through a material
to produce current, charges must flow continuously in a __________, __________ path
Symbol: ________
Unit: _________ (A or Amps)
1 A = 1 C/s
electrons
complete
unbroken I
Ampere
Ammeter

5. Current
Remember, the path that current flows through must be complete and unbroken. If there’s a break, the current will NOT flow!
Bueno!
No bueno.

6. What is voltage? Energy V Volts
_____________ available to move charges through a circuit
think of it as a force that pushes _________ through a circuit
voltage is also called the “potential difference” because there is a difference between the potential energy of the electrons in the voltage source and the electrons in the current
Symbol: ______
Unit: ___________ (V)
charges V
Volts

7. Voltage

8. Voltage
voltage is created by a voltage source, such as a _______, generator, solar panel, or ____________
battery
wall outlet

9. What is Resistance?
describes how ________ it is for the electrons to flow through a material
Conductors: ____ resistance, current flows ______
Insulators: _____ resistance, do not allow current to flow easily
Symbol: ______
Units: ________(Ω)
difficult
low
easily
high R
Ohms

10. Resistance
All sorts of items have resistance: light bulbs, doorbells… basically, whatever is “using” the energy in the circuit!

11. Resistance
There are four factors that affect the resistance of a wire:
Length: the longer a wire is, the ________ resistance it has
Diameter: the thicker a wire is, the _____ resistance it has
Material: Wires made of poor conductors have _____ resistance than wires made of good conductors
Temperature: As a wire gets hotter, its resistance _________.
more
less
more
increases

12. Resistors
A resistor is a device that reduces/controls the flow of electric current.

13. Current, Voltage, and Resistance

14. Current, Voltage, and Resistance

15. Bigger Voltage = Bigger Current
Voltage & Current
Bigger Voltage = Bigger Current

16. Resistance
Larger resistances need more voltage to have the same current

17. V = IR Ohm’s Law V = ________ (Volts) I = ________ (Amps)
Voltage
Current
Resistance

18. Current Depends On Voltage and Resistance
What happens to the amount of current if we increase the voltage?
The current _________.
increases

19. Current Depends On Voltage and Resistance
What happens to the amount of current if we increase the resistance?
The current __________.
decreases

20. Ohms’s Law Practice
A light bulb with a resistance of 5 ohms is connected to a battery. The current is 4 Amps. What is the voltage of the battery?

21. A 12 volt battery is connected to a circuit with a resistance of 4 ohms. What is the current?

22. A toaster is plugged into a wall outlet, such that V = 110 volts and I = 10 Amps. What is the toaster’s resistance?

23. Electric Power Review: Unit for power: ______ (W)
Basically, a power rating tells you something about the rate at which electrical energy is being converted into some other form (thermal, light, mechanical, etc.)
A 100 Watt light bulb is converting electrical energy into heat and light energy at a greater rate than a 40 Watt light bulb
Watts

24. Electric Power: The Variables
Use your MCAS FORMULA SHEET to determine what each symbol stands for
*notice that it is a capital “P” and a capital “V”
Symbol
Term
Units P
Watts (W) I
Amps (A) V
Volts (V)
Power
Current
Voltage

25. Electric Power: The Formula
Find the formula that uses these three variables (P, I, V)
P = IV
Alternate: P = I V = I (IR) = I2R
Twinkle, twinkle, little star, power equals I-squared-R

26. Electric Power Practice
A motor connected to 120 V draws a current of 10 A. What power is being consumed?

27. A blow-dryer that uses 1800 Watts is connected to a 120 volt outlet
A blow-dryer that uses 1800 Watts is connected to a 120 volt outlet. What current is passing through the blow dryer’s cord?

28. Series Circuits
13.1
In a series circuit, electrons flow through __________ _______.
Loads are connected in a chain, one after another in one continuous loop.
When one load does not work, the whole chain of loads ____________ because electrons ______ flow.
only one
path
stops working
cannot

29. Series Circuits
13.1

30. Series Circuits
13.1
The amount of current is the ________________ in a series circuit.
same at all points

31. Parallel Circuits
13.1
In a parallel circuit, electrons can flow through _______________ path.
Loads are connected in different branches that are connected to the energy source.
When a load does not work in one branch, the loads in the other branches _________________ because electrons ________________ another path.
more than one
continue to function
can flow through

32. Parallel Circuits
13.1

33. Parallel Circuits
13.1
Because there are multiple branches, the current is ___________________ in a parallel circuit.
not the same at all points

34. Circuits and Safety: Short Circuits
Short circuit: unintended direct contact between two points in an electrical circuit
electricity always chooses the “path of ______ resistance”
LOW resistance path = _____ current
least
high

35. Circuits and Safety: Short Circuits
Short circuits could cause some problems
Short circuits are dangerous because they can draw _____ amounts of current.
Battery gets drained _______
Wire will ________, possibly melting the insulation, which could start a fire
huge
faster
heat up

36. Circuits and Safety: Fuses
Fuses prevent dangerous levels of ________
Short circuits and _________________________ can both cause high currents
When the current is too high, the wire in the fuse melts
the circuit is ________
the current can no longer flow
the fuse must be _________
current
plugging in too many items
broken
replaced

37. Circuits and Safety: Circuit Breakers
Replacing fuses isn’t always the best solution
Many homes/power strips have circuit breakers
When the current is too high, the circuit breaker switch opens the circuit